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U1 = 1
r = 3
Un = U1 × r^n-1
729 = 1 × 3^n-1
729 = 3^n-1
3^6 = 3^n-1
6 = n-1
n = 7
Sn =
U1(rⁿ - 1)
------------
r - 1
1(3^7 - 1)
------------
3 - 1
2.187 - 1
------------
2
2.186
--------
2
Sn = 1.093
b.
U1 = 2
r = 2
Un = U1 × r^n-1
1.024 = 2 × 2^n-1
512 = 2^n-1
2^9 = 2^n-1
9 = n-1
n = 10
Sn =
U1 (rⁿ - 1)
-------------
r - 1
2 (2^10 - 1)
---------------
2 - 1
2 (1.024 - 1)
----------------
1
2 × 1.023
Sn = 2.046
c.
U1 = 4
r = 1/2
Un = U1 × r^n-1
1/32 = 4 × (1/2)^n-1
1/128 = (1/2)^n-1
2^-7 = 2^-n+1
-7 = -n + 1
n = 8
Sn=
U1 (1 - rⁿ)
-------------
1 - r
4 (1 - (1/2)^8)
------------------
1 - 1/2
4 (1 - 1/256)
-----------------
1/2
=4 (256/256 - 1/256) × 2
=8 ( 255/256)
=2.040/256
Sn = 7 284/256
Sn = 7 31/32
Yang bagian c yang jumlah seluruh suku ini khusus rasio kurang dari 1
Semoga membantu